The present invention generally relates to electrophotographic printing devices and more specifically to the reduction of toner leakage through seals in these devices.
Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form the desired image on the print medium, which is usually some type of paper. While the toner particles are solid, their small size (on the order of 3-15 microns) results in highly fluid properties. Once the toner is applied to the paper, the paper is advanced along a paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure.
FIG. 7 is a diagram of typical laser printing device 700 employing an ElectroPhotography (EP) process. For monochromatic printing, a single color of toner particles 701 are held in toner supply hopper 702. Toner particles 701 are typically small plastic (e.g. styrene) particles on the order of 5 microns (10xe2x88x926) meter in size. Agitator, or stirring blade, 703 is typically made of plastic or mylar and ensures toner particles 701 are uniformly positioned along developer sleeve 704 while inducing a negative charge onto the toner particles 701 in the range of xe2x88x9230 to xe2x88x9240 microcoulomb per gram (xcexcc/g). Developer sleeve 704 rotates in a counterclockwise direction about an internal stationary magnet 705 which acts as a shaft. Toner particles 701 are attracted to the rotating developer sleeve 704 by the magnetic forces of stationary magnet 705. Doctor blade 706 helps in charging toner particles 701 and metes out a precise and uniform amount of toner particles 701 onto developer sleeve 704 as its outer surface rotates external to toner supply hopper 702. Developer sealing blade 707 allows excess toner particles 701 affixed to developer sleeve 704 to be returned to toner supply hopper 702 without leakage.
Primary Charging Roller (PCR) 708 conditions Organic PhotoConductor (OPC) drum 709 using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum 709. Production of the uniform charge by PCR 708 also has the effect of erasing residual charges left from the previous cycle.
A major component of the EP process is OPC drum 709. OPC drum 709 is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PRC 708. Initially, the unexposed surface potential of the OPC drum 709 is approximately xe2x88x92600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC drum 709. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the aluminum substrate.
Laser beam 710 exposes OPC drum 709 one line at a time at the precise locations that will receive toner particles 701 (paper locations which correspond to the image being printed). OPC drum 709 is discharged from xe2x88x92600V to approximately xe2x88x92100V at points of exposure to laser beam 710, creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles 701 are magnetically attracted to rotating developer sleeve 704. Alternatively, if nonmagnetic toner particles 701 are used, developer sleeve 704 may comprise a foam roller to mechanically capture toner particles 701. In this case, an open cell foam roller may be included to apply toner particles 701 to developer sleeve 704. The still negatively charged toner held by developer sleeve 704 is attracted to the relatively positively charged areas of the surface of OPC drum 709 and xe2x80x9cjumpsxe2x80x9d across a small gap to the positively charged latent image on OPC drum 709 creating a developed image.
Paper to receive toner from OPC drum 709 is transported along paper path 711 between OPC drum 709 and transfer roller 712, with the developed image transferred from the surface of OPC drum 709 to the paper. The transfer occurs by action of transfer roller 712 which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles to move to the paper. Wiper blade 713 cleans the surface of the OPC drum 709 by scraping off the (untransferred or waste) toner particles 701 into waste hopper 715, while recovery blade 714 prevents the waste toner particles from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller 716 and pressure roller 717 where the toner particles 701 are melted and fused (or xe2x80x9cbondedxe2x80x9d) to the paper. Heated roller 716 and pressure roller 717 are together referred to as the fuser assembly.
One design consideration with imaging devices such as laser printers and copying systems is to minimize the leakage of toner or toner particles 701 from the toner supply hopper 702. As shown in FIG. 8, in its normal position, developer sleeve 704 has a toner supply on one side of seal 801 and the atmosphere on the other side of seal 801. Seals in this area are incorporated in an attempt to reduce or eliminate toner leakage.
Leakage sometimes occurs along a roller and at the ends of developer sleeve 704. Several methodologies have been used to reduce or eliminate such leakage. For example, some printers employ a foam or felt mechanical seal at the ends of developer sleeve 704 as a physical barrier to prevent toner particles 701 from leaking past the end of developer sleeve 704 and out of toner supply hopper 702. Alternatively, when the toner includes magnetic particles, such as in some black and white printers, magnetic seals may be provided at the ends of developer sleeve 704 to attract and capture toner particles 701 and to create a physical barrier, consisting of the toner particles 701, to prevent additional particles from leaking.
FIG. 8 shows the configuration of developer sleeve 704, toner particles 701 and seal 801. As shown, seal 801 is positioned between support 802 and developer sleeve 704. As developer sleeve 704 rotates, toner particles 701 are forced into junction 803 of seal 801 and developer sleeve 704. This action causes a buildup of toner and corresponding fluid pressure at junction 803 causing toner particles 701 to leak under, around and through seal 801.
Accordingly, a need exists for a system and a method for reducing toner leakage in a toner cartridge.
The present invention is directed to a system and method which comprises a toner cartridge including a developer roller having a cylindrical exterior surface with one or more peripheral tapering channels formed in the surface at one end of the developer roller. The channel has a narrow proximal end nearest the nearest end of the developer roller and a wide distal end toward the middle of the developer roller. The narrow proximal end of the channel extends deeper into the surface of the developer roller than does the wide distal end.